A patent to Synowicki et al., U.S. Pat. No. 8,692,985 is disclosed as particularly relevant to the present invention. It, however, does not disclose ellipsometric sensitivity being mostly to surface properties of a prism.
Another patent to Herzinger et al. U.S. Pat. No. 7,280,194 is disclosed as it describes methodology for determining Refractive Indicies of solid and fluid material's by placing a prism shaped material on a stage in a (θ)-2(θ) goniometer system, that rotates about an axis. This geometry makes the method thereof difficult to practice in a typical dual arm ellipsometer or the like system, in which the arms secure a source and a detector respectively, and rotate about a horizontally oriented axis to enable projecting a beam of electromagnetic radiation onto a sample on a centrally located stage. The present invention provides an approach for arriving at a similar result to that provided by Herzinger et al. 194, using an alternative sample investigation system arrangement.
In the context of the present invention, the method of determining the refractive index of a prism shaped material in U.S. Pat. No. 7,280,194, can be generally described as comprising the steps of:
a) providing a system comprising:                a1) a stage for supporting said prism shaped material;        a2) a fixed position source of a beam of electromagnetic radiation mounted on an source side of said stage for supporting said prism shaped material, and a detector of a beam of electromagnetic radiation mounted to a support arm on a detector side of said stage for supporting a prism shaped material; the positioning of said source of a beam of electromagnetic radiation defining an input angle of incidence to a source side of a prism shaped material when it is positioned on said stage, such that a beam of electromagnetic radiation from said source can be directed to enter the source side of said prism shaped material, be refracted thereby, pass through said prism shaped material and exit from said detector side of said prism shaped material at a refracted exit angle to said detector side of said prism shaped material, and then proceeds toward and enters said detector of beam of electromagnetic radiation;        a3) a means for rotating the detector side support arm to which said detector is attached, and a means for rotating said stage for supporting said prism shaped material, each through a range of angles.Said method then further comprises:        
b) mounting a prism shaped material to said stage, said prism shaped material having converging source and detector sides that form an apex angle “A” where they intersect;
c) while causing said fixed position source of a beam of electromagnetic radiation to provide a beam of electromagnetic radiation directed toward the source side of said prism shaped material at a fixed angle of incidence to the source side thereof, rotating said stage for supporting said prism shaped material and rotating said support arm on said detector side of said prism shaped material to which said detector is attached to selected positions, and monitoring the intensity of the beam entering said detector as a result.
And finally,
d) while monitoring intensity at the detector to enable determining the minimum deviation condition angle, identify the optimum rotation angles of said stage for supporting said prism shaped material and said support arm on said detector side of said prism shaped material to which said detector is attached, repeating step c) for multiplicity of rotations of said stage for supporting said prism shaped material and said support arm on said detector side of said prism shaped material to which said detector is attached until optimum angles of rotations for both the stage for supporting said prism shaped material and support arm on said detector side of said prism shaped material to which said detector is attached where the minimum deviation condition is achieved, (ie. where the intensity is maximum), and identifying the rotation angle of the support arm on said detector side of said prism shaped material to which said detector is attached as the optimum angle;
e) for the optimum angle determined in step d) applying the following formula:
      n    ⁢                  ⁢    2    =                    (                  sin          ⁢                                          ⁢                                    (                              A                +                                  θ                  ⁢                                                                          ⁢                  min                                            )                        /            2                          )                    sin        ⁢                                  ⁢                  (                      A            /            2                    )                      ⁢    n    ⁢                  ⁢    1  to determine n2.
Note, n1 and n2 are the refractive indicies of the ambient environment surrounding said prism shaped material, and of said prism shaped material, respectively.
It is noted that this approach utilizes a sample monitoring system in which, for each degree (θ) a beam of electromagnetic radiation from the source is changed to provide an angle of incidence to the sample, the detector angle is changed (2θ). That is, it utilizes a (θ)-(2θ) goniometer system. When the angle of incidence is (θ), the detector catches the beam at (2θ). This involves the detector arm angle being moved as a slave to the source arm angle and then locked in place. The present invention, it will be presented later in this specification, provides for each of the source and detector arms to be moved equal amounts in a (θ)-(θ) system arrangement, rather than utilize a (θ)-(2θ) system arrangement.
Said method involves investigating a solid prism shaped material, or can have an empty volume in said prism shaped material into which is caused to be present a liquid, the optical constants of which are desired to be determined.
Said method can involves using a source of electromagnetic radiation which is spectroscopic and wherein said method is repeated a plurality of times, for a plurality of wavelengths, to determine refractive index at each thereof.
Said method typically involves application of (θ)-(2θ) means for adjusting each of the source side and detector sides support arms through equal angles, by a mechanism that adjusts each of the source and detector side support arms by automatic simultaneous adjustment.
Even in view of the foregoing, need remains for an easy to practice method of characterizing surface properties of a prism, sequentially, or simultaneously with determining refractive indicies of a prism shaped material. This is especially the case when a spectroscopic beam of electromagnetic radiation is used and refractive indicies are to be quickly determined for a multiplicity of wavelengths in a single sweep of source and detector angles-of-entry and exit from the prism shaped material.